Due to the fast increase of recording density in the past decade, track widths continue to shrink into the deep sub-micron region. Currently, the magnetic track width has decreased to less than 0.2 μm for higher than 45 Gb/in2 recording densities. Different sensor stabilization schemes have been proposed to suppress the ever increasing demagnetizing effect on the sensor edge, including traditional hard biased abutted junction (ABJ) schemes and continuous pattern exchange (PEX) bias stabilization schemes as shown in FIGS. 1 and 2.
FIG. 1 shows a central GMR (giant magneto-resistance) stack made up of a bottom antiferromagnetic (AFM) layer 11 which serves to pin the magnetization of pinned layer 12. Non-magnetic spacer layer 13 (typically copper) sits atop layer 12 and is itself covered by free layer 14. Capping layer 15 completes the stack.
Longitudinal bias stabilization is provided by a ferromagnetic layer 17 whose magnetization is pinned by an adjacent antiferromagnetic layer. Prior art practice has been to locate the latter either directly above layer 17 (layer 18 in FIG. 1) or directly below it (layer 20 in FIG. 2). Also seen in both figures are the conductive leads 19.
In the standard hard bias ABJ case, in order to maintain good sensor stabilization, a thick hard bias layer is required, which causes magnetic hardening of the free layer as track width drops, leading to a decrease of the sensor output amplitude. On the other hand, if the hard bias layer becomes too thin, its magnetic properties deteriorate, and sensor stability worsens. To counter this, pattern exchange bias schemes have been proposed. The difficulty with these lies in the fact that it requires an etch back process in the sensor region, which needs to be controlled accurately. This is very difficult to achieve in a production environment. Also the reduction of the MRW (magnetic read width) is somewhat limited. So far the most effective way to reduce the MRW remains the ABJ structure. But this traditional hard bias scheme reduces the sensor sensitivity and MRW too much, and its extendability to future generations is limited.
It is known that exchange bias can be utilized in abutted junction as well. The problem with this is that a relatively large moment is needed to pin down the sensor edges effectively. Due to the inverse dependence of the exchange bias on the magnetic layer thickness, a large exchange bias has been difficult to achieve by the prior art.
A routine search of the prior art was performed with the following references of interest being found:
U.S. Pat. No. 6,324,037 B1 (Zhu et al.) shows a SV with an abutted junction and patterned exchange. U.S. Pat. No. 6,266,218 (Carey et al.) shows a MR with a Bottom SV and patterned exchange process. U.S. Pat. No. 6,275,362 B1 (Pinarbasi) describes a MR with a Bottom SV and buffer layer. U.S. Pat. No. 6,310,751 B1 (Guo et al.) shows a pattern exchange for a DSMR.